Video compression relies on two types of compressed video frames, Instantaneous Decoder Refresh frames (IDR-frames) and temporal predictive coding frames (P-frames). P-frames use inter-frame coding wherein a video frame is coded in terms of motion vectors and block coding referencing an already decoded frame (Reference frame). P-frames have the advantage over IDR-frames because they require less bandwidth.
The use of Long-Term Reference Frames (LTRFs) can increase video coding efficiency. Modern video standards such as H.264 allow as many as 16 reference frames to be retained at the decoder and used to predict future frames.
In some applications, such as video conferencing, periodic IDR-frames may not be necessary because no new decoder endpoints are added to a video conference after it starts. Without periodic IDR frames, there is no need to flush the decoder memory of reference frames. A long term reference memory may be used to store a very large number of reference frames. This may allow for high quality compression at lower bitrates. However, the time to search the memory for the best reference frame may be time-consuming.